The former navy reservist played "shoot 'em up" games like Call of Duty - with his best friend saying the games pushed his dark side

Crazed Aaron Alexis was treated for mental illness after playing violent video games for up to 18 hours day and night.

The 34-year-old told psychiatrists he heard voices in his head long before he went on the rampage at a US naval base and slaughtered 12 people before being shot dead himself.

Friends said the length of time he spent glued to the “shoot ‘em up” games on his computer, including the popular Call of Duty, triggered his dark side that had previously landed him in trouble with the police on gun crimes.

But despite his psychiatric problems and arrests for violence, the IT contractor was never declared mentally unfit by the US Navy – a move that would have stripped him of the security pass that allowed him to drive unchallenged into the ­Washington base and carry out his murderous mission.

And as a result, his gun licence was also never rescinded.

Friend Nutpisit Suthamtewakul said “hard-core drinker” former navy reservist Alexis became so hooked on video games he would have to take him food as he would not tear himself away to eat.

He added: “He could be in the game all day and all night. I think games might be what pushed him that way.”

Alexis had worked at Suthamtewakul’s Happy Bowl Thai restaurant in Fort Worth, Texas.

His best pal added: “He always had this fear people would steal his stuff so that’s why he would carry his gun all the time.

"He would carry it when he was helping out in the restaurant which scared my customers.”

Happy Bowl customer Chris Childs said he would often chat to Alexis about violent video games.

He said the killer was “really into” Call of Duty and World of Warcraft.

Mr Childs added: “There were a couple of guys I worked with that were kind of into shooter games, but by the time a new one came out, he would know a lot about the game.”

Another friend, Michael Ritrovato, told how he saw twisted Alexis playing the part of a killer in the games.